Going at relativistic speeds will fry anything living or electronic in massive x-ray and gamma radiation. Add to that collisions with dust particles, which will have enormous abrasive effects on the starship.

The reason aliens aren’t here already seems to be proof that there are, either no aliens (or very, very few) or there are no loopholes in physics for FTL or warp to span the giant distances involved in space(travel).

My training is in biology and computing, not in physics, but my understanding is that the feasibility of the Bussard ramjet is still very much up in the air – the amount of hydrogen in the interstellar medium in our part of the galaxy is much lower than Bussard had originally assumed, which makes the ramjet idea potentially much more difficult to achieve.

Absent that, an ion drive would allow for lengthy periods of thrust and offers the potential for relativistic speeds, but at the cost that you do have to drag along all your fuel which cuts into the size of your payload considerably.

Since we don’t know the exact parameters of what kinds of environments are suitable for abiogenesis, nor do we know anything about the planet’s composition, I’d be hesitant even to speculate on whether life could exist on that planet.

http://www.youtube.com/watch?v=BNLfNe12BKE

http://en.wikipedia.org/wiki/Fermi_paradox

Conditions, from the laws of physics, to the placement of Earth….everything had to evolve in the way it did because, yes, it’s just far too dangerous out there, and still is. For other species in the universe to have the same kind of life, especially many like most science-fiction portray…gets sort of implausible when you think about it.

Your starship can’t go any faster than whatever is shooting out the tailpipe. Yet CERN’s Large Hadron Collider can boost charged particles up near the speed of light.

So a charged particle accelerator many orders of magnitude larger than the LHC will be able to boost at one g for a 14-year-long trip to Tau Ceti. And you will only experience something over two years of time during the trip.

Back in the age of sail, the Spanish and Portuguese explorers circled the globe in tiny wooden ships of only a few hundred tons of displacement — and they did that in about two years.

If they could stand to be cooped up all that time while eating nothing but sea biscuit and salt pork with a little rind of moldy, worm-eaten cheese, then we can stand the strain of the voyage in a ship the size of an asteroid.

Our starships will have geodesic domes covering great pastures where cows and sheep graze, and other domes covering growing fields of corn, wheat, soybeans, and chickpeas. Not to mention the immense rice paddies in other BuckyFullerDomes. And oh yes, let’s take along an orchard of lemon trees to avoid the dread scurvy.

but if gravity was double, how would that affect the formation of animal size….?? animals with stronger gravity would at least be stronger. http://en.wikipedia.org/wiki/Gravitational_biology

The primary exception would be if you’re able to use solar sails for much of your acceleration and deceleration – in that case you wouldn’t have to have (much) fuel on board (a little may be needed just to manage the sail and to keep the ship’s basic systems going). I have a hard time picturing how you could reach such a high percentage of the speed of light using primarily solar sails though – they’d have to be truly massive.

Bussard ramjets, anyone?

It would be a long shot for sure but might give us important info sharing without traveling anywhere.

However, assuming that life on Earth is pretty typical of life elsewhere, the assumption would have to be that if the planet is larger that the largest potential size for organisms on that planet would probably be smaller. The larger mass of the planet would most likely imply a higher surface gravity (depending on the density of the planet, of course), and so the structure of the organisms on the planet would have to withstand more weight. Since the strength of a particular material is roughly proportional to it’s cross-sectional area, any structural components of the organisms (bones, wood, etc) would need to be proportionately larger than for similar organisms on Earth. Similarly, if the organism is an animal it would require more muscle power (either larger muscles or arranged to get better mechanical advantage, again assuming that the basic structure of the muscles was similar to that of Earthly animals). Naturally, if the atmosphere is sufficiently dense, there may be a buoyancy effect that will offset some of these considerations, and in general for similar reasons they won’t apply as much to aquatic life as they do to land-based life (not unlike the situation on Earth).

The result of these effects is that larger size will tend to be more limiting than it is on Earth. Still, the largest organisms on Earth are quite large, so we’re not talking about a major limitation.

Going at space shuttle speed we can expect to get there in 446,400 years. Anyone that who can’t fathom that should be willing to sign up for that mission. No worry’s now about how were screwing up this planet. We can move right next door.

So the question really becomes, once life starts, how many civilizations make it long enough to be able to utilize technology and engineering to directly avoid cataclysmic galactic events? Not many. Not many at all I’d say. It’s just dangerous out there.

I’d like to note that nobody has demonstrated that all we need to have intelligent life, or just life, in a place is the right conditions and enough time. It’s really kind of a crazy idea if you think about it, a bunch of rocks, some water, give it a few billion years and you have Manhattan.
I suspect we’re missing something important there, which would probably go a long way towards answering the question “where is everybody?”

For those of you out there who are interested in the search for other planets, Wikipedia has a list of all the latest discoveries, including all the facts known about all the host stars and the masses of the newly discovered planets.

http://en.wikipedia.org/wiki/List_of_exoplanetary_host_stars